5.2 Natural selection Flashcards
What does natural selection depend on within populations?
Variation amongst members of the same species
What is variation?
The presence of variety - the differences between individuals
What are the 4 types of variations?
- Genetic
- Continuous
- Discontinuous
- Environmental
What are the 3 causes of genetic variation?
- Mutations
- Meiosis
- Sexual reproduction
How does mutations cause genetic variation?
Changes to the DNA sequence by gene mutations lead to new alleles, enlarging the gene pool of the population
How does meiosis cause genetic variation?
Independent assortment and crossing over
* New combinations of alleles by breaking up the existing combination in a diploid cell
How does sexual reproduction cause genetic variation?
Random fusion of gametes from two unrelated individuals
* Allows mutation that occured in different individuals to be brought together
What are adaptations?
Characteristics that make an individual suited to its environment and way of life
What are structural, behavioural and physiological adaptations?
Structural: Physical differences in biological structure
Behavioural: Differences in patterns of activity
Physiological: Differences in detection and response to surrounding
Why is it important not to imply purpose to adaptaions?
According to evolutionary theory adaptations develop by natural selection, not with the direct purpose of making an individual suited to its environment.
What is the Malthusian Dilemma?
- Population size increeases exponentially
- Resources only increase linearly
- More species produce more offspring than the environment can sustainably support
- This leads to competition within a population, causing the population growth to slow
What are the consequences of species producing more offspring than the environment can support?
- Struggle for survival
- Competition for resources
- Not every individual will obtain enough to allow them to survive and reproduce
Which type of individuals are more likely to survive and produce more offsrping when resources are competitive?
Individuals that are better adapted and they pass on the characteristics to their offsrping
How does natrual selection allow for evolution?
Natural selection increases the frequency of characteristics that make individuals better adapted and decreases the frequency of other characteristics leading to changes within the speces - evolution by natural selection
What are some selection pressures dependent on the population size?
- Predators
- Availability of resources (e.g. shelter, water)
- Nutrient supply (i.e. food source)
- Disease/pathogenic spread
- Accumulation of wastes
What are some selection pressures that are not affected by the population size?
- Phenomena (e.g. natural disasters)
- Abiotic factors (e.g. temperature, CO2 levels)
- Weather conditions (e.g. floods, storms, etc)
What is the galapagos finches an example of? (adaptive or convergent and why)
Adaptive radiation
* Darwin hypothesised that ‘fromm an original paucity of birds in this archipelago, one species had been taken and modified for their different ends’
What is heritability?
The portion of the variation due to genes is called heritability
How long after an antibiotic is introduced do the bacteria show resistance?
Within a few years
Does resistance to antibiotic spread?
Yes, resistance to the antibiotic spreads to more and more species of pathogenic bacteria
* in each species the proportio of infections that are caused by a resistant strain increases
How is evolution present in the resistance of antibiotics?
- During the time over which antibiotics have been used to treat bacterial diseases there have been cumulative changes in the antibiotic resistance properties of populations of bacteria.
- The development of antibiotic resistance is therefore an example of evolution
What is antibiotic resistance due to?
Genes in bacteria and so it can be inherited
What are 4 causes of the rapid evolution of multiple antibiotic resistance?
- Widespread use of antibiotics, both for treating diseases and in animal feeds used on farms
- Bacteria can reproduce very rapidly, with generation time of less than an hour
- Populations of bacteria are often huge, increasing the chance of a gene for antibiotic resistance being formed by mutation
- Bacteria can pass genes on to other bacteria in several ways, including using plasmids, which allow one species of bacteria to gain antibiotic resistance genes from another species
